1. Field of Invention
The present invention relates to a movable stage apparatus capable of precise movement, and particularly relates to a stage apparatus movable in one linear direction capable of high accuracy positioning and high speed movement, which can be especially favorably utilized in a microlithographic system. This invention also relates to an exposure apparatus that is used for the transfer of a mask pattern onto a photosensitive substrate during a lithographic process to manufacture, for example, a semiconductor element, a liquid crystal display element, a thin film magnetic head, or the like.
2. Description of Related Art
When a semiconductor element or the like is manufactured, a projection exposure apparatus is used that transfers an image of a pattern of a reticle, used as a mask, onto each shooting area on a wafer (or a glass plate or the like) on which a resist is coated, used as a substrate, through a projection optical system. Conventionally, as a projection exposure apparatus, a step-and-repeat type (batch exposure type) projection exposure apparatus (stepper) has been widely used. However, a scanning exposure type projection exposure apparatus (a scanning type exposure apparatus), such as a step-and-scan type, which performs an exposure as a reticle and a wafer are synchronously scanned with respect to a projection optical system, has attracted attention.
In a conventional exposure apparatus, a reticle stage, which supports and carries the reticle, which is the original pattern, and the wafer to which the pattern is to be transferred, and the driving part of the wafer stage are fixed to a structural body that supports a projection optical system. The vicinity of the center of gravity of the projection optical system is also fixed to the structural body. Additionally, in order to position a wafer stage with high accuracy, the position of the wafer stage is measured by a laser interferometer, and a moving mirror for the laser interferometer is fixed to the wafer stage.
Furthermore, in order to carry a wafer to a wafer holder on the wafer stage, a wafer carrier arm that takes out a wafer from a wafer cassette and carries it to the wafer holder, and a wafer carrier arm that carries the wafer from the wafer holder to the wafer cassette, are independently provided. When the wafer is carried in, the wafer that has been carried by the wafer carrier arm is temporarily fixed to and supported by a special support member that can be freely raised and lowered and that is provided on the wafer holder. Thereafter, the carrier arm is withdrawn, the support member is lowered, and the wafer is disposed on the wafer holder. After this, the wafer is vacuum absorbed to the top of the wafer holder. When the wafer is carried out from the exposure device, the opposite operation is performed.
As described above, in the conventional exposure apparatus, the driving part of the wafer stage or the like and the projection optical system are fixed to the same structural body. Thus, the vibration generated by the driving reaction of the stage is transmitted to the structural body, and the vibration is also transmitted to the projection optical system. Furthermore, all the mechanical structures were mechanically resonate to a vibration of a predetermined frequency, so there are disadvantages such that deformation of the structural body and the resonance phenomenon occurred, and position shifting of a transfer pattern image and deterioration of contrast occurred when this type of vibration is transmitted to the structural body.
Furthermore, because the wafer stage moves over a long distance from the carrier arm for carrying in and out of the wafer to the exposure position, it is necessary to provide an extremely long moving mirror for the laser interferometer. Because of this, the weight of the wafer stage becomes relatively heavy and the driving reaction becomes large because a heavy motor with a large driving force is needed. Furthermore, in order to improve throughput, when the moving speed and acceleration of the stage needs to be increased, the driving reaction becomes even larger. In addition, as the weight and acceleration of the stage increase, the heating amount of the motor increases, and there is a disadvantage such that measurement stability or the like of the laser interferometer deteriorates.
Furthermore, in the case of carrying the wafer into and out of the exposure apparatus, the wafer is temporarily fixed and supported on the top of a special support member, so carrying in and out of the wafer consumes time. This causes deterioration of throughput. Additionally, as one example, because giving and receiving of the wafer is performed between the carrier arms, the probability of the wafer being contaminated is high, and the probability of having an operation error when the wafer was given and received is high. Furthermore, the number of carrier arms is a major point governing the size of the carrier unit, so the carrier path becomes long when giving and receiving of the wafer is performed between the carrier arms on the carrier path. Additionally, a floor area (foot print) that is needed for the exposure apparatus also becomes large.
In wafer steppers, the alignment of an exposure field to the reticle being imaged affects the success of the circuit of that field. In a scanning exposure system, the reticle and wafer are moved simultaneously and scanned across one another during the exposure sequence.
To attain high accuracy, the stage should be isolated from mechanical disturbances. This is achieved by employing electromagnetic forces to position and move the stage. It should also have high control bandwidth, which requires that the stage be a light structure with no moving parts. Furthermore, the stage should be free from excessive heat generation which might cause interferometer interference or mechanical changes that compromise alignment accuracy.
Commutatorless electromagnetic alignment apparatus such as the ones disclosed in U.S. Pat. Nos. 4,506,204, 4,506,205 and 4,507,597 are not feasible because they require the manufacture of large magnet and coil assemblies that are not commercially available. The weight of the stage and the heat generated also render these designs inappropriate for high accuracy applications.
An improvement over these commutatorless apparatus was disclosed in U.S. Pat. No. 4,592,858, which employs a conventional XY mechanically guided sub-stage to provide the large displacement motion in a plane, thereby eliminating the need for large magnet and coil assemblies. The electromagnetic means mounted on the sub-stage isolates the stage from mechanical disturbances. Nevertheless, the combined weight of the sub-stage and stage still results in low control bandwidth, and the heat generated by the electromagnetic elements supporting the stage is still substantial.
Even though the current apparatus using commutated electromagnetic means is a significant improvement over prior commutatorless apparatus, the problems of low control bandwidth and interferometer interference persist. In such an apparatus, a sub-stage is moved magnetically in one linear direction and the commutated electromagnetic means mounted on the sub-stage in turn moves the stage in the normal direction. The sub-stage is heavy because it carries the magnet tracks to move the stage. Moreover, heat dissipation on the stage compromises interferometer accuracy.
It is also well known to move a movable member (stage) in one long linear direction (e.g. more than 10 cm) by using two of the linear motors in parallel where coil and magnet are combined. In this case, the stage is guided by some sort of a linear guiding member and driven in one linear direction by a linear motor installed parallel to the guiding member. When driving the stage only to the extent of extremely small stroke, the guideless structure based on the combination of several electromagnetic actuators, as disclosed in the prior art mentioned before, can be adopted. However, in order to move the guideless stage by a long distance in one linear direction, a specially structured electromagnetic actuator as in the prior art becomes necessary, causing the size of the apparatus to become larger, and as a result, generating a problem of consuming more electricity.
It is an object of the present invention to make it possible for a guideless stage to move with a long linear motion using electromagnetic force, and to provide a light weight apparatus in which low inertia and high response are achieved.
It is another object of the present invention to provide a guideless stage apparatus using commercially available regular linear motors as electromagnetic actuators for one linear direction motion.
It is another object of the present invention to provide a guideless stage apparatus capable of active and precise position control for small displacements without any contact in the direction orthogonal to the long linear motion direction.
It is another object of the present invention to provide a completely non-contact stage apparatus by providing a movable member (stage body) that moves in one linear direction and a second movable member that moves sequentially in the same direction, constantly keeping a certain space therebetween, and providing the electromagnetic force (action and reaction forces) in the direction orthogonal to the linear direction between this second movable member and the stage body.
It is another object of the present invention to provide a non-contact stage apparatus capable of preventing the positioning and running accuracy from deteriorating by changing tension of various cables and tubes to be connected to the non-contact stage body that moves as it supports an object.
It is another object of the present invention to provide a non-contact apparatus that is short in its height, by arranging the first movable member and the second movable member in parallel, which move in the opposite linear direction to one another.
It is another object of the present invention to provide an apparatus that is structured so as not to change the location of the center of gravity of the entire apparatus even when the non-contact stage body moves in one linear direction.
Another object of this invention is to provide an exposure apparatus that can perform an exposure with high accuracy by reducing the effects of vibration on a projection optical system or the like that occurs when the wafer stage or the like is driven.
Another object of this invention is to provide an exposure apparatus that suppresses the amount of heat generated by the driving part of the wafer stage, to perform positioning of the driving part of the wafer stage with high accuracy, and to maintain the measurement stability of a position measurement device or the like.
Another object of this invention is to provide an exposure apparatus with high throughput that can carry a wafer to an exposure apparatus without temporarily fixing the wafer, and without giving and receiving of the wafer between wafer carrier arms.
In order to achieve the above and other objects, embodiments of the present invention may be constructed as follows.
An apparatus that is capable of high accuracy position and motion control utilizes linear commutated motors to move a guideless stage in one long linear direction and to create small yaw rotation in a plane. A carrier/follower holding a single voice coil motor (VCM) is controlled to approximately follow the stage in the direction of the long linear motion. The VCM provides an electromagnetic force to move the stage for small displacements in the plane in a linear direction perpendicular to the direction of the long linear motion to ensure proper alignment. This follower design eliminates the problem of cable drag for the stage since the cables connected to the stage follow the stage via the carrier/follower. Cables connecting the carrier/follower to external devices will have a certain amount of drag, but the stage is free from such disturbances because the VCM on the carrier/follower acts as a buffer by preventing the transmission of mechanical disturbances to the stage.
According to one aspect of the invention, the linear commutated motors are located on opposite sides of the stage and are mounted on a driving frame. Each linear commutated motor includes a coil member and a magnetic member, one of which is mounted on one of the opposed sides of the stage, and the other of which is mounted on the driving frame. Both motors drive in the same direction. By driving the motors slightly different amounts, small yaw rotation of the stage is produced.
In accordance with another aspect of the present invention, a moving counter-weight is provided to preserve the location of the center of gravity of the stage system during any stage motion by using the conservation of momentum principle. In an embodiment of the present invention, the drive frame carrying one member of each of the linear motors is suspended above the base structure, and when the drive assembly applies an action force to the stage to move the stage in one direction over the base structure, the driving frame moves in the opposite direction in response to the reaction force to substantially maintain the center of gravity of the apparatus. This apparatus essentially eliminates any reaction forces between the stage system and the base structure on which the stage system is mounted, thereby facilitating high acceleration while minimizing vibrational effects on the system.
By restricting the stage motion to the three specified degrees of freedom, the apparatus is simple. By using electromagnetic components that are commercially available, the apparatus design is easily adaptable to changes in the size of the stage. This high accuracy positioning apparatus is ideally suited for use as a reticle scanner in a scanning exposure system by providing smooth and precise scanning motion in one linear direction and ensuring accurate alignment by controlling small displacement motion perpendicular to the scanning direction and small yaw rotation in the scanning plane.
An exposure apparatus according to another aspect of this invention includes a projection optical system support member that supports a projection optical system, so that the projection optical system rotates within a specified area, taking a reference point as a center. Therefore, even if vibration from a substrate stage and a mask stage is transmitted to the projection optical system, the position relationship between the object plane (mask) and the image plane (substrate) is not shifted. Thus, it is possible to prevent position shifting of the pattern to be transferred, and highly accurate exposure can be performed.
Furthermore, a mask stage that moves a mask, a structural body that supports this mask stage and the projection optical system, and a substrate stage that moves a substrate are provided. The projection optical system support part (the structural body) has at least three flexible support members extending from the structural body, and the extending lines of each support member cross at the reference point. In this case, even if vibration is transmitted to the projection optical system, the projection optical system is minutely rotated taking the reference point as a center. Therefore, it is possible to prevent position shifting of the pattern to be transferred to the substrate. Furthermore, the support members are flexible, so the minute vibration can be reduced and the deterioration of contrast of a pattern to be formed can be prevented.
An exposure apparatus according to another aspect of this invention controls the mask base so that the mask base moves at a specified speed in a direction opposite to the moving direction of the mask stage. This reduces the effects to the structural body of the driving reaction of the mask stage. Additionally, the excitation of mechanical resonance is controlled, and the vibration transmitted to the structural body and the projection optical system can be reduced. Therefore, exposure with a high accuracy can be performed.
In an exposure apparatus according to another aspect of this invention, by having an elastic member at both ends of a guide axis, when the substrate table performs constant velocity reciprocation on the guide axis, the kinetic energy of the substrate table is converted to potential energy and is stored in the elastic members. Therefore, the energy to be consumed when the substrate table is reciprocated at constant velocity is mainly only the energy to be consumed in the viscosity resistance of the substrate table with respect to air. The only heat generated is the heat from when the elastic members are deformed. Therefore, it is possible to control the heating amount of the driving part when the substrate table moves at constant velocity.
Furthermore, when the elastic member has first magnetic members disposed at both ends of the guide axis and second magnetic members disposed corresponding to the first magnetic members, by the attraction of the first and second magnetic members, when the substrate table is still-positioned at an end of the guide axis, it is possible to reduce the thrust of the driving part of the substrate table required to oppose the resistance of the elastic member. Thus, the heating amount of the driving part can be controlled when the substrate table is still-positioned.
In an exposure apparatus according to another aspect of this invention, by controlling the length of the support legs that can be freely extended and retracted in the support direction, the tilt angle of the substrate table and its position in the height direction can be controlled, and highly accurate exposure can be performed as the surface of the substrate is aligned within the image plane.
Furthermore, when the mask and the substrate are synchronously and moved during exposure, the tilt angle of the scanning surface of the substrate stage of the structural body in the scanning direction, the tilt angle in the non-scanning direction, and the height are detected. When the support legs that can be freely extended and retracted are controlled based upon the detection result, highly accurate scanning exposure can be performed as the surface of the substrate is aligned within the image plane.
Furthermore, when the rotation angle of the substrate stage about the optical axis of the projection optical system and the position shifting amount are detected, and the position of the mask stage or the substrate stage is controlled based upon this detection result, the positioning between the surface of the substrate and the image plane can be performed with high accuracy.
In an exposure apparatus according to another aspect of this invention, a visco-elastic body exists between the support member and the structural body, so it is possible to reduce the vibration from the floor on which the exposure device is disposed. Therefore, exposure can be performed with high accuracy.
In an exposure apparatus according to another aspect of this invention, at least one groove is provided in the substrate table, and a substrate can be disposed on the substrate table without the substrate carrier arms contacting the substrate table. That is, there is an advantage such that the substrate can be carried into and out from the exposure device, without temporarily fixing and supporting the substrate on the substrate table, and throughput can be improved.
Furthermore, when the substrate carrier mechanism has at least two substrate carrier arms and substrate storage case support members, the substrate carrier arms can be freely moved in the three directions such as a rotational direction about the optical axis of the projection optical system, the horizontal direction, and the vertical direction, and the substrate storage case support member can be freely moved in the vertical direction, there are advantages such that the substrate stage can be moved below the substrate carrying-out arms or the substrate carrying-in arms, the substrate can be carried to the exposure device without transferring the substrate between the substrate carrier arms, and the probability of problems occurring during the carrying and the probability of foreign objects attaching to the wafer can be reduced.
Other aspects and features and advantages of the present invention will become more apparent upon a review of the following specification taken in conjunction with the accompanying drawings wherein similar characters of reference indicate similar elements in each of the several views.